The usual reason for this issue where the LMS rejects a ZIP file because it cannot find the imsmanifest.xml file is due to the way the ZIP file is created. When Captivate creates the ZIP file it always has the imsmanifest.xml file at the root level inside the ZIP file.
However, if you were to publish from Captivate to HTML and then zip the FOLDER containing the published HTML, then the imsmanifest.xml file would end up being one level BELOW the root level inside the ZIP file.
Most people don't realise that the way you create the ZIP file will affect whether or not the LMS accepts it. If possible, just let Captivate create the SCORM ZIP by specifying this in the Publish settings. If for some reason you must first publish to HTML and then later use WinZip or some other app to create the final ZIP file, the trick is to just go inside the folder that holds the published HTML, select everything there, and then create the ZIP. Don't just ZIP the folder itself. Hope that helps.
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